PSI - Issue 77

L.A. Lingnau et al. / Procedia Structural Integrity 77 (2026) 26–33 Author name / Structural Integrity Procedia 00 (2026) 000–000

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with the mechanical test results. To complement the metallographic analysis with a quantitative component, a subset of the acquired images was subjected to image segmentation. For this purpose, Zeiss ZEN Core software was used in combination with the integrated AI-based segmentation module, ZEN Intellesis. The images were imported for training, and different regions were manually classified into the corresponding categories. In this context, the classes were defined as voids, manganese sulfides and the steel matrix. 3. Results and discussion 3.1. Damage accumulation under cyclic tension-tension loading and compression-compression loading To investigate the load path-dependent behavior as well as the accumulation of damage, both cyclic tension-tension and cyclic compression-compression loading experiments were conducted. During these tests, the damage evolution was monitored microscopically in-situ. Fig. 3a shows the nominal stress plotted over the duration of the experiment for the tension-tension loading. The specimen was subjected to three loading cycles, reaching a maximum nominal stress of 450 MPa. This procedure enables the analysis of progressive material degradation as a function of loading direction and cycle number. Comparable experiments were performed under cyclic compression-compression loading. Fig. 3b shows the nominal stress plotted over the duration of the experiment for the compression-compression loading. The specimen was also subjected to three loading cycles, reaching a maximum nominal compressive stress of - 450 MPa. It should also be noted that SEM images were captured specifically during the intervals in which the applied stress was held constant. In the plots showing nominal stress over time, these segments were cropped out to improve clarity and make the loading sequence easier to understand ( Fig. 3a-b ). This approach enables a detailed assessment of damage accumulation at defined stress levels throughout the experiment.

Fig. 3. Representation of nominal stress σ Ν over time for a) tension-tension tests and b) compression-compression tests.

To analyze and quantify damage accumulation during the cyclic tension-tension loading experiments, SEM images were acquired at the same specimen location specifically at the same manganese sulfide at 0 MPa and 450 MPa at each cycle. Fig. 4a shows the initial state, Fig. 4b depicts the condition after the first loading cycle, and Fig. 4c illustrates the final state after completion of the test. A manganese sulfide, marked with a red box in the center of each image, serves as the reference point for damage tracking. The red-marked area is shown in magnified form in Fig. 4d-f . Based on this image section, damage around and inside the manganese sulfide was quantified using an AI-based image segmentation approach (Lingnau et al., 2024b). To exclude artifacts resulting from changes in working distance due to specimen deformation or other measurement uncertainties, the ratio of damage proportion to manganese sulfide proportion f DS was introduced as a normalized damage metric ( Eq. 1 ). = (1)